Large numbers of homes are wired for cable TV. The characteristic impedance of the coaxial cable used in such a system is typically 75 ohms. In these cable systems, all coaxial cable, active and passive electronic devices used in the system are designed to function with an electrical impedance of 75 ohms.
Cable systems are typically constructed to allow for a coaxial cable connection to cable subscribers. These systems use standard coaxial cables having a cylindrical conductive housing or shield as a first circuit path, and a coaxial center conductor as a second circuit path. A single cable is typically run to each home or apartment, and then an internal splitter is used to allow for multiple "outlets" or coaxial cable jacks that are usually mounted in wall plates. To use a particular coaxial outlet or jack, a coaxial cable having a mating male connector is run from the wall jack to a television set or VCR. However, it is not uncommon for one or more of the jacks to be left "open" or uncoupled to a TV, VCR, or other electronic device.
When a coaxial connector or jack is left "open" or unconnected, the uniform impedance characteristics of the cable system are disturbed, causing undesirable reflection and radiation of electrical signals into and out of the center connector. Such undesirable signals are introduced back down the cable, and are sometimes seen as "ghosts" on the television. While spurious signals rarely become a critical problem for cable television systems, these undesirable signals are critical when the cable system is used for telephone or digital data communication. Specifically, if any of the coaxial cable jacks in the house are left open, significant errors can occur in modem or other telephone data communications that take place over the cable system.
One solution has been to provide a "self-terminating" coaxial connector or jack to reduce signal problems induced through open cable jacks. Such "self-terminating" coaxial connectors can be switched to a "terminated" condition when the coaxial cable jack is left open or uncoupled. A terminated condition exists when the center conductor of the coaxial cable jack is connected to its conductive shield through a termination circuit element having the same or approaching the same characteristic impedance as the coaxial connector and cable, which for most cable system is 75 ohms. Thus, in many "self-terminating" cable connectors a 75 ohm resister connects the center conductor and the cylindrical conductive housing when the connector is left uncoupled.
Several versions of "self-terminating" cable connectors or jacks are known to exist. Usually, an internal switching arrangement is provided in the cable connector so that the two circuit paths of the coaxial cable are connected by a terminating resistance when the jack is left uncoupled. In that way, the end of the line is not allowed to remain in an open state. Exemplary coaxial cables and terminating connectors are described in various references, including U.S. Pat. Nos. 2,965,858; 3,525,056; 3,768,063; 3,784,950; 3,873,785; 4,660,921; 4,971,569; 5,030,122; 5,073,123; 5,076,797; 5,090,915; 5,237,293; and 5,340,325, each of which is incorporated herein by reference.
Previous efforts using "self-terminating" connectors have suffered from problems associated with the internal switching arrangements used to terminate the circuits. In "self-terminating" connectors, the terminating resistance must be connected between the outer housing and the central conductor at a position such that they do not interfere with the insertion of a cooperating male coaxial connector. Often as a consequence of this, when the male connector is withdrawn and the self-terminating resistance is connected, a small unconnected portion of the central connecting stub remains beyond the point where the terminating resistance is connected. In such devices, it is impossible to avoid a certain amount of capacitive coupling between this dead end stub portion and the outer cylindrical housing. Further, the stub reflects energy back down the line, which is a deficiency for the telephone industry, which often operate above 60 megahertz.
Another disadvantage of many of the existing "self-terminating" cable connectors is that they often require the use of custom female connectors or jacks. However, the vast majority of cable-ready homes throughout the country do not have the custom female connectors or coaxial cable jacks installed at the outlet wall plates, but rather, use a standard cable jack. Accordingly, to convert existing standard configurations to the custom connections and jacks required by many of the known forms of self-terminating connectors would require many man-hours unscrewing wall plates, disconnecting the coaxial cable jack from the wall plate, disconnecting the jack from the cable located inside the wall, connecting a new custom "self-terminating" female jack, and reassembling the components. Furthermore, replacement of the standard female connector with custom "self-terminating" female jacks could also require cable companies and consumers to replace or purchase an associated adapter for the corresponding custom male connectors.
Yet another disadvantage with prior "self-terminating" connectors is that the "switch" used to provide the terminating resistance is internal. Over time, the moving parts of the internal "switch" can wear and become inoperative. Replacing these worn connectors would also require the removal of the wall plate from the wall, disconnecting the coaxial cable jack from the wall plate, disconnecting the jack from the cable located within the wall, replacing a new jack on the cable and reassembling the components.
Another solution to the "open" jack problem had been to install an easily removable "terminating" endcap on any cable jacks that were not in use. Such "terminating" endcaps are also designed to provide a terminating resistance between the two circuit paths of the coaxial cable when the endcaps are connected to the cable jack. A homeowner must remove the endcap from the jack whenever they want to connect a cable thereto. These endcaps must also be replaced by the homeowner whenever the cable is removed from the jack to prevent an "open" situation from occurring. Additionally, these endcaps are often lost or misplaced when they are removed from a jack. In other cases, the person removing a cable from the jack either does not know, or forgot that the endcap should be replaced. As a result, jacks are often left in an "open" condition, even when the "terminating" endcaps were previously provided. Often the replacement costs for lost and misplaced endcaps and the cost in man-hours to remind homeowners to use the endcaps can become burdensome.
The present invention overcomes the above disadvantages without departing from the standard coaxial cable configuration by providing a connecting outlet in which the voltage standing wave ratio (VSWR) is maintained very close to unity so as to virtually eliminate reflection of spurious signals from the connector outlet. An apparatus is provided to "terminate" or "close" the cable jack with a "terminating resistance" applied at the very end of and external to the cable, thereby eliminating any unconnected portions of the central conductive circuit path. Even when the "terminating resistance" is removed from the jack, the apparatus cannot be lost or misplaced because the apparatus is attached to a wall plate or other location proximate to the cable jack. Additionally, since the apparatus is located near the jack, the apparatus acts as a reminder to replace the apparatus when the jack is not in use. In some forms, the apparatus even acts as a "self-terminating" connection. The present invention is compatible with existing standard coaxial cable jacks and connectors allowing the invention to be used with existing cable systems. Retrofitting such a system merely requires the replacement of the standard wall mounting plate, or the addition of a piece external to the wall mounting plate. Furthermore, all moving parts are external to the cable connector. Most repairs would merely require exchanging a piece that is external to the wall mounting plate.